﻿<p>A rational B-spline surface with knots is a piecewise parametric rational surface described in terms of control points, and associated weight values.</p>

<p>The surface is to be interpreted as follows:</p>

<blockquote>
<big>&sigma;</big><img src="../../../figures/ifcbsplinesurface-math2.gif" align="middle" alt="formula" border>
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<blockquote class="note">
NOTE&nbsp; Entity adapted from <strong>rational_b_spline_surface</strong> in ISO 10303-42.
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<blockquote class="history">
HISTORY&nbsp; New entity in IFC4.
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